ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

ANDREAS LANG
Optical-dating of Late Glacial and Holocene sediments:
test cases of water born sediments from central Europe
Forschungsstelle Archaomerrie, Heidelberger Akademie
der Wissenschaften, Max-Planck-Institut fur Kernphysik,
Saupfercheckweg 1, D-69117 Heidelberg, Germany
Accurate dating is essential for any time-related question in
geomorphology. For Late Glacial and Holocene sediments
usually this is achieved by 14C or dendrochronological-dating,
if organic materials are present. Unfortunately, such
lucky cases are rare.
Luminescence dating methods allow age determination of
a mineral grain's last exposure to daylight. This requires
sufficient bleaching during transportation and sedimentation
before a grain is buried. Due to the poor light conditions
during the formation of many water laid sediments,
thermoluminescence (Tl) dating is hardly promising. The
major advantage of optical - and infrared-stimulated luminescence
(Osl/Irsl) over Tl is the restriction to very lightsensitive
electron traps. This results in an improved dating
precision and, in many cases, allows applications to sediments,
which were only shortly exposed to light. Daylight
exposure of mineral grains during transportation and sedimentation
is highly complex at the «single grain» - scale
and it is hard to determine deterministica]. Between
others, it is dependent on sunlight spectrum and flux (e.g.
geographical location, weather conditions, time of the
day), transport conditions (i.e, water depth, turbulences,
suspended sediment, coagulation of grains) and the duration
of the exposure.
In this study an empirical approach was chosen: optical dating
was tried on sediments of various depositional environments'
for which independent age control were available.
The aim of the study is to find out for which types of
sediments optical dating may be applied successfully and
to further develop a powerful tool for resolving time-related
questions in geomorphology.
The sediment types range from fluvial, colluvial, limnic to
littoral deposits. The results show that Irsl and Osl are suitable
for dating colluvial, limnic, littoral and, in many cases,
fluvial sediments in the time span up to several 10 ka.
These deposits represent specific characteristics which can
easily be determined by geomorphologists.
ABDELLAH LAOUINA
Desertification of eastern Moroccan steppes:
geomorphological aspects
Department of Geography, University Mohammed V, Rabat, Morocco
In the steppic environment of the eastern Moroccan high
plains, a wide variety of complex ecosystems coexist and
are" in relation with both natural and human factors. The
morphological aspects are important to explain the surface
changes in term of available resources and of stability of
the whole geosystem.
Many methods have been applicated to assess these surface
changes and namely the desertification process. To describe
the environmental potential, morpho-pedological survey
permits the delimitation of units in term of quality of
soils with a special mention about the eroded horizons.
The survey of the sanded up and of the eroded surfaces
permit to make a relation between processes wich affect
the same region, but with selective action. The assess of the
soil biomass production, the vegetation cover density and
the loss observed in this production and density during the
last years attest the loss of soil and of fertility, wich has also
been evaluated by the measurement of the runoff and soil
erosion. By aerial photo remote sensing, the increase of
surfaces affected by hydric or eolian erosion, permits to assess
the speed of degradation and to establish a map of risks
and of critical situations.
The process of desertification, in this weakly inhabited region,
is linked to the important changes observed in the
land occupation and in the systems of soil utilisation. In this
arid region, where the land is covered by Artemisia berba
alba for the low surfaces affected by sheet wash and by Stipa
tenacissima for the drained plateaux and pediments, already
eroded with the outcrop of hard calcretes and of pebbles,
the sedentarisation of the nomades and the progress of
cultivated areas changed the water balance of the surface in
some spaces and explain the increase of soil loss. The barley
cultivations, wich seem to be a success in the first years,
decline rapidly in productivity and explain the frequent
abandon of bare lands, after a short period of erosion, namely
in case of the occurence of a high magnitude event.
The constitution of crusts on the surface leads to more runoff
and more erosion. The wind affects wider spaces and
explains the constitution of two kinds of surfaces: gravel
ones and sandy ones. The question of sustainability is then
formulated. The second question is the choice of adapted
technics to this hard milieu, to prevent erosion and to ensure
water infiltration and to the complex social context.
EDGARDO M. LATRUBESSE1, ANTONIO ROSSI 2
& ELENA FRANZINELLI 3
Geomorphology of the Pacaas Novos Range,
Southwestern Amazonia, Brazil,
1Universidade Federal do Acre, BR 364 km 4, Campus Universitario,
69915-900, Rio Branco, AC, Brazil
2 Universita di Modena, L. Eufemia 19, Modena, Italy.
3 Universidade do Amazonas, Caixa Postal 885,
69011-970, Manaus, AM, Brazil
The geomorphologv of the Pacaas Novos range was surveyed.
The Pacaas Novos range is situated in the state of
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